The present invention relates to a method for the preparation of a patterned photoresist layer on the surface of a substrate and a photoresist composition used therefor. More particularly, the invention relates to a method for the preparation of a patterned photoresist layer having excellent resolving power and resistance against dry etching on the surface of a substrate and a photoresist composition therefor.
In the electronics of recent years, LSIs, ultra-LSIs and other extremely fine electronic devices can be manufactured only by the aid of fabrication technologies in the submicron range or finer by the photolithographic techniques of patterning using a photoresist material so that it is eagerly desired to develop a photoresist composition of high sensitivity capable of giving an extremely fine patterned photoresist layer with high resolving power.
While photoresist compositions used in the electronic technology are classified into positive-working and negative-working ones, the major trend in the technology is in the use of a negative-working photoresist composition which can be crosslinked and insolubilized when irradiated with actinic rays to form a solubility difference between the irradiated and unirradiated areas. In order to work satisfactorily, negative-working photoresist compositions must satisfy several requirements in the properties including that (1) the composition should be crosslinked with high sensitivity when it is irradiated with actinic rays, e.g. ultraviolet, far ultraviolet, electron beams and X-rays, and insolubilized, (2) the irradiation by the actinic rays can produce a change as great as possible in the molecular structure and physical properties or, in particular, in the solubility behavior of the composition, (3) the polymeric constituent of the composition should have an adequate molecular weight with a molecular weight distribution as narrow as possible in order to obtain a high sensitivity and high resolving power, (4) the glass transition point T.sub.g of the polymer should be high enough, (5) good adhesion should be obtained between the photoresist layer and the substrate surface, (6) the photoresist layer should withstand and little be affected by dry etching, and so on.
The negative-working photoresist compositions currently on use mostly comprises a cyclized rubber as the polymeric constituent but none of the commercially available photoresist compositions can satisfy the above mentioned requirements, in particular, in respect of the resolving power and the resistance against dry etching.